This protocol seeks to explore the effects of level source of dietary protein on bone turnover in pre-and post-menopausal women. Initial data indicate that when dietary protein is increased from low-normal to high-normal in young women with intestinal calcium absorption and bone turnover increase, whereby in the low-normal diet secondary hyperparathyroidism is observed. To more precisely quantitate the relative contributions of bone and gut to these induced changes in mineral metabolism, we will employ stable calcium isotopic methodologies in pre- and post menopausal women.